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We studied the structural, elastic, electronic, dynamic and optical properties of scandium and yttrium nitrides in the zinc blend structure. The GGA, LDA and GGA-PBESOL approaches, as well as the HSE hybrid functional, were used in the representation of the electronic exchange and correlation effects. The lattice constant, the bulk modulus and its pressure derivative calculated in the HSE hybrid approach are predictions. The elastic constants and B/G ratio infer that ScN and YN are elastically stable and ductile in nature. ScN and YN in the zinc blend structure show an isotropic linear compressibility and anisotropic Young's modulus, shear modulus and Poisson's ratio. The anisotropy and hardness in ScN and YN compounds are more pronounced in the LDA approach. The X–X (W–W) direct band gap in scandium (yttrium) nitride translates its semiconductor character in the zinc blend structure. The N: p orbit and small contribution of Sc: d (Y: d) site are responsible to the optical modes, while Sc: d (Y: d) site and small contribution of N: p orbit are the sign of acoustical modes. The absorption peaks are assigned to photo transitions energies from maximum valence band to minimum conduction band.

This study investigated the effect of aging on the precipitation and kinetics of second phase Mg17Al12 in AZ91 magnesium alloy (Mg-9 wt% Al-1 wt% Zn), using X-ray diffraction, microhardness measurements and differential scanning calorimetric analysis (DSC). With the last instrument, the all samples were heated from room temperature to 400 °C, at heating rates of 10–30 °C/min. The results were supplemented by measuring the average of activation energies, using isothermal treatments by Johnson–Mehl–Avrami (JMA) methods and by non-isothermal treatments using Ozawa, Boswell, Kissinger, Mahadevan, Augis and Bennett methods, were around 67.18 and 62.02 kJ/mol. The frequency factor k0 calculated by the isothermal treatment is equal to 1.24 109 s−1. In non-isothermal treatment, the numerical factor m and the Avrami parameter n is estimated to be approximately equal to 3 and 2.79 respectively. This value corresponding that the bulk nucleation with a constant number of nuclei was dominant in three-dimensional (polyhedron) controlled by interface reaction. Keywords: AZ91, DSC, Mg17Al12, Precipitation, Activation energy

In this paper, we present a detailed theoretical investigation on the structural, elastic, electronic and optical properties of the perovskite oxides SrThO3 and SrZrO3 by using the pseudo-potential plane wave (PP-PW) method. The computed lattice constants of SrXO3 (X = Th and Zr) are in excellent agreement with the available experimental data. SrThO3 and SrZrO3 are direct (Γ–Γ) and indirect (Γ–R) band gap semiconductors, respectively. Under pressure effect a crossover between the indirect band gap (R–Γ) and the direct band gap (Γ–Γ) curves occurs at about 35 GPa for SrZrO3, resulting in the energy minimum of direct gap (Γ–Γ) for this compound. The covalence in the Zr–O and Th–O bonds arises due to the hybridization between O–p and Zr–d (Th–d) states. Under pressure effect, the threshold energy becomes slightly greater (smaller) for SrZrO3 (SrTO3) for 3.21 (2.28) eV and the main peaks are shifted towards higher energies. Although the positions of all peaks shifted under pressure, they still have the same type as those at zero pressure, with decreasing the intensity of the main peaks.

The lead free halides double perovskites show a particular interest in the conception of perovskites solar cells. We predicted the lattice constant and the atomic Wycko position of these lead free halide double perovskites Cs2AgBiX6 (X = Br, Cl) under pressure effect. The alloying ability of crystal, elastic constants and related parameters, electronic and optical properties have been studied using pseudo potential plane wave method based on the density functional theory. The investigated lead free halide double perovskites Cs2AgBiX6 (X = Br, Cl) show a weaker resistance to compression along the a-axis. This result also proves the existence of a directional bonding between atoms and a weaker resistance to compression along the a-axis The band structure indicates that Cs2AgBiX(X = Br, Cl) are X–L indirect gap semiconductors. Our computed bulk modulus and its pressure derivative of double perovskites Cs2AgBiX6 (X = Br, Cl) are predictions. The calculated elastic constants of Cs2AgBiX6 (X = Br, Cl) at equilibrium and under pressure effect are predictions.

We focus on detailed investigation of structural, elastic, electronic, and optical properties of inorganic complex chloride and bromide CsInCl3 and CsInBr3 in zinc blende structure within GGA and LDA. The lattice constant for CsInCl3 and CsInBr3 computed with GGA approach is closer to experimental value, where the estimated error is 0.2% and 0.28%. Elastic moduli at equilibrium and under pressure effect for CsInCl3 and CsInBr3 are studied for the first time. CsInCl3 and CsInBr3 are elastically stable, ductile, show lower hardness and have dominantly covalent bonding character. Band structure of CsInCl3 and CsInBr3 computed with GGA (LDA) indicate an indirect band gap L-X: 1.583 eV (1.186 eV) and L-W: 0.831 eV (0.75 eV) which traduce their semiconducting character. We report the predicted GGA and LDA electron and hole effective masses m e ∗ and m p ∗ for CsInCl3 and CsInBr3. The Cs: p site is empty in the first conduction band, consequently, transitions occur from Cl: p (Br: p) state to Cs: p site. Lattice constant and bond lengths d X − I n of CsInX3 (X = Cl, Br) are proportional to the radius of X atom. The anisotropy is more pronounced in the LDA approach for CsInCl3 and CsInBr3. The indirect band gap L-X becomes L-W at about 0.5 GPa for inorganic complex chloride CsInCl3, while CsInBr3 has a tendency to the metallic character.

The effect of additional Mg on the microstructure, mechanical properties, and transformation kinetics during aging in Al–3.3 wt.% Cu alloy was studied. The compositions and microstructure were examined by X-ray diffraction, Differential scanning calorimetry (DSC) and scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS). The results show that the Mg in the Al–Cu alloy mainly precipitated to the grain boundaries during the process of transformation and formed a ternary Al2CuMg metallic compound and the rate of discontinuous precipitation reaction decreases with increasing concentration of Mg. The activation energy of crystallization was evaluated by applying the Kissinger equation.

We report the performance of glass/Mo/CuInSSe(CISSe)/(Zn2SnO4, CdS, SnS2)/ZnO thin films structures using solar cell capacitance simulator (SCAPS). Thin films solar cells with CuInSSe absorber layer reduce the cost and have comparable performance parameters with the conventional ones. The temperature effect on efficiency and fill factor is less noticeable in solar cell with Zn2SnO4 buffer layer. The average temperature gradient of CdS, SnS2 and Zn2SnO4 based cells value is -0.317 %/K, -0.533 %/K and -0.539 %/K. An efficiency of 18.53 % has been achieved with Zn2SnO4 buffer for Voc, Jsc and FF of 0.5153 V, 45.4 mAcm−2 and 79.17. The desired thickness of the CuInSSe (CISSe) absorber layer is estimated as 1.8 μm. The best performance obtained with Zn2SnO4 buffer can be explained by its higher transmission in the short wavelength range because its high gap 3.35 eV compared to those of CdS 2.4 eV and SnS2 2.24 eV.

We have calculated the bond lengths d F 3 → F 5 , 7 , 8 , d F 4 → F 5 , 6 , 8 , d F 2 → F 5 , 7 , 8 , d F 1 → F 6 , 7 , 8 , d F 1 → 8 − Y 1 , 2 , 3 , d F 9 → Y 1 , 2 , 3 , d F 1 → 8 − F 9 and single-crystal elastic stiffness constants, Cij and polycrystalline elastic moduli at different pressures by using GGA-PBE, GGA-PBESOL and LDA approach for cubic YF3. Yttrium fluoride is found to be elastically stable in the pressure range 0–40 GPa. Shear modulus, linear compressibility and Poisson's ratio have maximum and minimum values along with different crystallographic directions, which explain their predicted anisotropy. The direct Γ-Γ band gap value 5.082 eV indicates towards the insulating character of YF3. The broad band gap is a sign that this compound should function as an emission center. We predicted the first and second-order pressure coefficients of direct and indirect band gaps using the GGA-PBE, GGA-PBESOL and LDA approaches. The estimated volumetric thermal expansion coefficient, constants volume and constant pressure heat capacities and entropy at zero pressure and 300 K are 1.66 × 105 K−1, 82.56 J m o l − 1 K − 1 and 83.59 mol-1 K−1, respectively. The edge of the optical absorption is located at 48.5 nm which is caused by the V1−C1 transition at the Γ point in the Brillouin zone that corresponds very well to the direct band gap at Γ- Γ.

Using ab initio spin-polarized density functional theory calculations, the structural, elastic and thermodynamic properties of the orthorhombic and hexagonal phases of the iron carbide Fe7C3 were investigated. The calculated ground-state lattice parameters are in good agreement with the available corresponding theoretical and experimental data. The single-crystal and polycrystalline aggregate elastic constants, sound velocities, Debye temperature, brittle/ductile character and elastic anisotropy have been estimated. The calculated bulk modulus values of both considered phases are very close and are approximately equal to 262 GPa, which classifies the title compounds among the hard materials. The temperature and pressure dependencies of the unit-cell volume, bulk modulus, volume thermal expansion coefficient, isochoric and isobaric heat capacity, and Debye temperature were investigated using the quasi-harmonic Debye model.

We studied the profiles of the micro hardness in the nuances 9SMn28, 42CrMo4 and CK45, which have a rapid decline to the depth 0.1 mm, and then slowly decrease to the value of the characteristic of the casting material. The surface layer contains mostly the iron nitrides phases FeyN (y = 1, 2, 3, 4). We use first principles to study the electronic and magnetic properties of some structural phases. We calculated the lattice parameters of all the compounds; our results show good agreement with other calculations. The estimated formation energies first show a decrease then an increase with the nitrogen content. The contribution of the PDOS is due to the Fe-3d and N-2p states in Fe(1–4)N. We used experimental and theoretical studies to determine all of the phases existing in a nitride layer.

First-principles density functional calculations were performed to investigate the structural parameters, elastic moduli and related properties, electronic band structure and optical properties of three LaOAgS-type barium silver fluoride chalcogenides BaAgChF (Ch denotes the chalcogenides S, Se and Te). The calculated structural parameters are in good accordance with the existing experimental data. The single-crystal and polycrystal elastic moduli were determined via the strain–stress technique. The investigated compounds show a strong anisotropic behaviour of the structural and elastic parameters. The calculated electronic band structure using the Tran–Blaha modified Becke–Johnson potential reveals that the three considered systems are large direct band gap semiconductors. The assignments of the energy band electronic states and chemical bonding character were accomplished with the help of the l-decomposed atomic densities of states diagrams. Frequency-dependent polarized optical functions were computed for an energy range from 0 eV to 30 eV. The microscopic origin of the electronic states that is responsible for the optical spectra structures were determined. The optical spectra exhibit a considerable anisotropy. Several trends in the variation of the considered physical properties with the atomic number Z of the chalcogenide Ch element in the BaAgChF series are observed.

We report structural, elastic, electronic, dynamical and optical properties of beryllium selenide in zinc blend and NiAs phases. The zinc blend structure is the most stable at room temperature and equilibrium hydrostatic pressure. The HSE hybrid functional underestimates the lattice parameters compared to the GGA-PBE and LDA, but gives a fundamental gap closer to its experiment value. We derive bulk modulus, shear modulus, Young's modulus and Poisson's ratio using Voigt, Reuss and Hill approximations. Computed elastic constants in NiAs structure are predictions. Waves velocities for beryllium selenide in zinc blend (NiAs) phase along [100], [110] ([100], [110], [111]) directions are predictions. The indirect band gap Γ-X (2.852 eV) and Γ-K (0.536 eV) for BeSe in zinc blend and NiAs structures translates the semiconductor nature. Hybridization occurs between Se: p and Be: s states at the top of the valence band and traduces the covalent bonding character. The first conduction band is quite wide in both structures, where the contribution is due to Se: p, Se: s and Be: s sites. The electronic transition occurs from Se: p orbital of valence band to Be: s site of conduction band. Absorption peaks are attributed to the photo transition energies from the maximum valence band to the minimum conduction band under ultra violet light irradiation.

We report ab initio density functional theory calculations of the structural, elastic, electronic and optical properties of the double perovskite oxides Sr2AlXO6 (X=Ta, Nb, V). We have predicted a direct Г–Г band gap in Sr2AlXO6 (X=Ta, Nb) and an indirect Г–X band gap for Sr2AlVO6. The fundamental band gap increases linearly when the pressure is enhanced in the range 0–20 GPa. The frequency dependent of complex dielectric function, absorption, reflectivity and electron energy loss function were investigated in the range 0–40 eV. Features such as lattice constant, bulk modulus, elastic constants, band structure, total and local densities of states have been computed.

The results of fundamental properties of zinc-blende ZnSe1−xOx ternary system and related binaries (i.e. ZnSe and ZnO) are reported using the ab initio pseudopotential-density-functional calculations. Features such as lattice constant, bulk modulus, energy gaps and electron effective mass have been determined and their variation as a function of oxygen concentration has been presented and discussed. A good agreement is obtained between the calculated results and existing experimental data. It is found that the lattice constant of the material of interest violates the Vegard's law. The information gathered from the present study could be useful for solar cells technological applications.

We present calculations of the structural, elastic and electronic properties of nonferrous Ti, Zr, and Hf pure metals in both parent and martensitic phases in bcc and hcp structures respectively. They are based on the generalized gradient approximation (GGA) within the density functional theory. The shear modulus, Young's modulus and Poisson's ratio for Ti, Zr, and Hf metals have were calculated and compared with the corresponding experimental values. Using elastic constants obtained from calculations under the GGA, the bulk modulus along the crystallographic axes of single crystals is calculated. This is in good agreement with experiment for Ti and Zr, whereas the hcp structure for Hf is a prediction. At zero temperature and zero pressure, the bcc crystal structure is found to be mechanically unstable for Ti, Zr, and Hf. In our calculations the hcp structure is correctly found to be stable at the equilibrium volume. In the electronic density of states, the smaller n(EF) is, the more stable the compound is, in agreement with the results obtained from the total energy minimum.

The PLANE WAVE pseudo-potential method within density functional theory (DFT) has been used to investigate the structural, elastic, electronic and optical properties of XCaF3 (X = K and Rb) insulating. The studied compounds show a weak resistance to shear deformation compared to the resistance to the unidirectional compression. KCaF3 and RbCaF3 are considered ductile. The elastic constants and related parameters were predicted. The stiffness is more important in KCaF3, whereas, the lateral expansion is more important in RbCaF3. KCaF3 and RbCaF3 have R- Г indirect band gap. The main peaks in the imaginary part of the dielectric function correspond to the transition from the occupied state F−p to the unoccupied states Ca: s or K, Rb: p. At lower energies, KCaF3 and RbCaF3 show the same optical properties. Under pressure effect, the peaks of imaginary part of dielectric function were shifted toward high energy.

The structural, electronic and elastic properties of the M 2 SiC phases were studied, where M are 3d, 4d, and 5d early transition metals. The valence electron concentration (VEC) effect of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W on these properties was examined. The C 44 saturates for a VEC value in surrounding of 8.5 for each serie. Hf-s, Ta-s and W-s electrons mainly contribute to the density of states at the Fermi level, and should be involved in the conduction properties. The distortion increases with increasing VEC and decreasing k c / k a factor except for the series M=Ti, V and Cr, where it is lower at the VEC value of 8.5 (it follows a parabolic variation). The M 2 SiC was characterized by a profound anisotropy for the shear planes (1010) and compressibility in the direction is higher than that along the cone except for W 2 SiC, where it is lower.

The quaternary iridium based hydrides NaAeIrH6 (Ae = Ca, Ba and Sr) are promising candidates as hydrogen storage materials. We have studied the structural, elastic, electronic, optical and thermodynamic properties of NaAeIrH6 (Ae = Ca, Ba and Sr) within the generalized gradient approximation, the local density approximation (LDA) and mBj in the frame of density functional perturbation theory. These alloys have a large indirect Γ–X band gap. The thermodynamic functions were computed using the phonon density of states. The origin of the possible transitions from valence band to conduction band was illustrated. By using the complex dielectric function, the optical properties such as absorption, reflectivity, loss function, refractive index and optical conductivity have been obtained.

Electronic band structure and lattice dynamical properties of CaxMg1−xS alloys in the rock-salt phase have been investigated. The calculations are performed in the framework of ab initio pseudo-potential approach within the generalized gradient approximation. Reasonable agreement is generally obtained between our results and the available experimental observations and previous calculations. The deviation of the alloy lattice constant and bulk modulus from linearity has been examined and discussed. Fundamental band gaps and Г–X and Г–L separations in higher-lying conduction bands are predicted. In agreement with reflectivity spectrum and recent optical absorption spectrum measurements, CaS in the rock-salt phase is found to be an indirect band-gap (Г–X). Similarly to CaS, the electronic band structure calculations showed that MgS is also an indirect band-gap (Г–X) semiconductor. However, a system transition between indirect and direct structures has been predicted in the Ca concentration range 0.12–0.83. Upon alloying the phonon modes are significantly changed showing that the longitudinal optical–transverse optical (LO–TO) splitting becomes narrower as one proceeds from pure rock-salt MgS to pure rock-salt CaS.

Special quasi-random structure (SQS) was used to investigate the structural, electronic, and optical characteristics of the binary and ternary beryllium chalcogenide alloys. The computations were performed using the pseudopotential technique. The GGA-WC scheme was applied to study the structural and optical features of these present alloys, while the HSE06 hybrid functional was used to correct the underestimation of the electronic band structure. The optimized lattice constants and bulk modulus demonstrate a non-linear tendency with increasing x concentration. The phase transition may occur for all ternary alloys at x = 0.5 with the orthorhombic assumed crystal system. The ternary alloys of BeO1−xAx (A = S, Se) at 0.5 ⩽ x ⩽ 1 have an indirect band gap, while BeO1−xTex0.5 ⩽ x ⩽ 1 manifest a metallic demeanor using HSE06 formalism. The optical spectra were computed and discussed in detail. Furthermore, the thermodynamic stability of the studied compounds was examined using the miscibility critical temperature.

The structural, elastic, electronic and optical properties of the gallium monohydrides BaGaXH (X=Si, Ge, Sn) have been investigated by means of first principles calculations. The low values of the B/G ratio of these compounds correspond to the brittle nature, which is due to the hydrogen presence. The bulk modulus, Young's modulus, shear modulus decrease from Si to Sn for BaGaXH (X=Si, Ge, Sn) in the same column in the periodic table. Also the Debye temperature of these compounds has a relative high θ D value indicating that they possess good thermal conductivity. The mean sound velocities have a progressive decrease from silicon (Si) to tin (Sn).

The alkaline platinum hydrides are considered the most promising as hydrogen storage materials. The alloying ability of crystal, elastic constants and related parameters, electronic and optical properties have been studied using pseudo-potential plane–wave method based on the density functional theory. The investigated compounds show a weaker resistance to compression along the principal a-axis and their resistance to shear deformation is lower than the resistance to the unidirectional compression. The band structure indicates that A 2 PtH 6 (A=K, Rb and Cs) are X–X direct gap semiconductors. The effective electron mass at equilibrium has been predicted towards X–Γ, X–W and L–W directions. The strong hybridization between Pt-d and H-s states in the upper valence band translates the existence of covalent bonding character in these compounds. The static optical dielectric constant is inverse proportional to the fundamental gap.

Structural, electronic and optical properties of the ZnSc2S4 and CdSc2S4 cubic spinels have been investigated by means of the full-potential (linearized) augmented plane wave plus local orbitals based on density functional theory. The exchange-correlation potential is treated by the GGA–PBEsol [J.P. Perdew, A. Ruzsinszky, G.I. Csonka, O.A. Vydrov, G.E. Scuseria, L.A. Constantin, X. Zhou, K. Burke, Phys. Rev. Lett. 100 (2008) 136406] and the recently proposed modified Becke–Johnson potential approximation (mBJ) [F. Tran, P. Blaha, Phys. Rev. Lett. 102 (2009) 226401], which successfully corrects the band-gap problem found with GGA for a wide range of materials. The obtained structural parameters are in good agreement with the available experimental data. This gives support for the predict properties for ZnSc2S4 and CdSc2S4. The band structures reveal that both compounds are semiconductor with a direct gap. The obtained gap values show that mBJ is superior for estimating band gap energy. We have calculated the electron and hole effective masses in different directions. The density of states has been analyzed. Based on our electronic structure obtained using the mBJ method we have calculated various optical properties, including the complex dielectric function ɛ(ω), complex index of refraction n(ω), reflectivity coefficient R(ω), absorption coefficient α(ω) and electron energy-loss function L(ω) as functions of the photon energy. We find that the values of zero-frequency limit ɛ1(0) increase with decreasing the energy band gap in agreement with the Penn model. The origin of the peaks and structures in the optical spectra is determined in terms of the calculated energy band structures.

We present results of ab initio calculations concerning lattice dynamical and thermal properties of MgS, CaS and their ternary mixed crystals CaxMg1−xS in zinc-blende structure. Results for the phonon modes, dielectric constants, Frohlich coupling parameter, polaron effective mass, entropy and heat capacities are given for CaxMg1−xS within a composition range 0–1. Generally good agreement is obtained between our results and data available in the literature. Other case, our results are predictions.

M 3 X (M=Cr, V; X=Si, Ge) compounds are studied using first-principles calculations based on the Density Functional Theory (DFT). It is found that the bulk of Cr 3 X (X=Si, Ge) compounds are comparable to those of Al 2 O 3 , the nearest-neighbor distance D M−M and D M−X in these compounds increase and the bulk modulus decrease, there is a strong interaction between M and M (M=Cr the interaction is stronger). Also the interaction between M (M=Cr, V) and X (X=Ge) is negative, an anti-bonding-type interaction is dominant between these atoms.

Based on the density functional theory as implemented in the Abinit code under the virtual crystal approximation, the lattice constant, bulk modulus, elastic constants, gap energies, electron effective mass, the dielectric constants and born effective charge in In{sub 1-x-y}Al{sub x}Ga{sub y}As have been calculated with both GGA and LDA in the range 0{

We have carried out a first-principles density functional study of the structural, elastic and thermodynamic properties for the SnMg2O4, SnZn2O4 and SnCd2O4 cubic normal spinel structures. We have calculated the equilibrium structural parameters: the lattice constant and internal structural parameter. These results agree very well with experimental data. We have investigated the zero-pressure single-crystal and polycrystalline elastic constants and their related properties, confirming prior theoretical results for SnMg2O4 and predicting values for SnZn2O4 and SnCd2O4. The pressure dependence of the elastic constants Cij can be fit by a straight line over the range 0–30 GPa. Thermal and pressure effects on some macroscopic properties of SnMg2O4, SnZn2O4 and SnCd2O4 are predicted using the quasi-harmonic Debye model in which the lattice vibrations are taken into account.

Some physical properties of the cubic perovskites CsXF3 (X = Ca, Sr and Hg) have been investigated using pseudopotential plane-wave method based on the density functional theory. The calculated lattice parameters within GGA and LDA agree reasonably with the available experimental data. The elastic constants and their pressure derivatives are predicted using the static finite strain technique. We derived the bulk and shear moduli, Young's modulus, Poisson's ratio and Lame’s constants for ideal polycrystalline aggregates. The analysis of B/G ratio indicates that CsXF3 (X = Ca, Sr and Hg) are ductile materials. The thermal effect on the volume, bulk modulus, heat capacity and Debye temperature was predicted.

A theoretical study of the structural, electronic, optical and thermodynamic properties of Na x Rb 1 −x H and Na x K 1 −x H ternary alloys in NaCl phase has been carried out using the first-principles method. We modeled the alloys at some selected compositions with ordered structures described in terms of periodically repeated supercells. The dependences on the composition of the lattice constant, band gap, dielectric constant, refractive index, Debye temperature, mixing entropy and heat capacities were analyzed for x =0, 0.25, 0.50, 0.75 and 1. The lattice constants of Na x Rb 1 −x H and Na x K 1 −x H exhibit a marginal deviation from Vegard's law. A strong deviation of the bulk modulus from linear concentration dependence was observed for both alloys. We found that the composition dependence of the energy band gap is highly non linear and the large bowing coefficient for Na x Rb 1− x H is sensitive to the composition. Using the approach of Zunger and co-workers, the microscopic origins of the gap bowing were detailed and explained. The thermodynamic stability of these alloys was investigated by calculating the phase diagram. The thermal effect on some macroscopic properties was investigated using the quasi-harmonic Debye model. There is a good agreement between our results and the available experimental data for the binary compounds, which is a support for those of the ternary alloys that we report for the first time.

The structural, elastic, electronic and thermal properties of the MAX phases Ti2SiC and Cr2SiC are studied by means of the pseudo-potential plane wave method within GGA and LDA. The effect of pressure on the normalized lattice constants a/a0 and c/c0 and the internal parameter z is investigated. Our results of elastic constants, sound velocities and Debye temperature are predictions. The Ti2SiC and Cr2SiC compounds behave as ductile material and show a stronger anisotropy. The analysis of the band structure and density of states show that these compounds are electrical conductors, having a strong directional bonding between Ti and C and Cr and C atoms assured by the hybridization of Ti–d and Cr–d atom states with C–p atom states. The thermal effect on the primitive cell volume, bulk modulus, heat capacities CV and CP were predicted using the quasi-harmonic Debye model.

A computed investigation on the structural, elastic, electronic, phonon frequencies and thermal properties of AlxScyB1−x−yN quaternary alloys in the zinc-blend phase has been made with first-principles methods. The information on the lattice constant, lattice matching to AlN substrate and energy band gaps is indispensable for various practical applications. We have studied the effect of Sc concentration y (y = 0, 0.152, 0.303, 0.455 and 0.607) on the lattice constant, bulk modulus, elastic constants C11, C12 and C44, band gaps, optical phonon frequencies (ωTO and ωLO), static and high-frequency dielectric coefficient ɛ(0) and ɛ(∞) and dynamic effective charge Z*. We remark an important deviation from the linear concentration dependence of the lattice constant and bulk modulus. The shear moduli, Young's modulus, Poisson's ratio were estimated in the frame work of the Voigt–Reuss–Hill approximation. The resistance to changes in bond length and lateral expansion in AlxScyB1−x−yN increase with increasing y concentration. We observe that at y concentration about 0.11, the Г–X indirect fundamental gap becomes Г–Γ direct fundamental gap in AlxScyB1−x−yN. There is well agreement between our results and the experiment data for AlN binary compound which is a support for those of the quaternary alloys that we report for the first time.

A theoretical study on the structural, elastic, electronic and lattice dynamic properties of Al x Y y B 1− x − y N quaternary alloys in zinc-blend phase has been carried out with first-principles methods. Information on the lattice parameter, the lattice matching to available substrates and energy band-gaps is a prerequisite for many practical applications. The dependence of the lattice parameter a , bulk modulus B , elastic constants C 11 , C 12 and C 44 , band-gaps, optical phonon frequencies ( ω TO and ω LO ), the static and high-frequency dielectric coefficients e (0) and e ( ∞ ) and the dynamic effective charge Z ⁎ were analyzed for y =0, 0.121, 0.241, 0.362 and 0.483. A significant deviation of the bulk modulus from linear concentration dependence was observed. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young's modulus, Poisson's ratio are numerically estimated in the frame work of the Voigt–Reuss–Hill approximation. The resistance to changes in bond length and lateral expansion in Al x Y y B 1− x − y N increase with increasing y concentration. We observe that at y concentration about 0.035 and 0.063, Al x Y y B 1− x − y N changes from brittle to ductile and Γ–X indirect fundamental gap becomes Γ–Γ direct fundamental gap. There is good agreement between our results and the available experimental data for the binary compound AlN, which is a support for those of the quaternary alloys that we report for the first time.

Various physical properties of the cubic perovskite-type oxide BiScO3 have been investigated using the pseudo-potential plane-wave (PP-PW) method based on the density functional theory (DFT). The computed equilibrium lattice parameters agree well with the available theoretical data. The elastic constants and their pressure dependence are predicted using the static finite strain technique. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature are numerically estimated in the framework of the Voigt–Reuss–Hill approximation for BiScO3 polycrystalline aggregate. The analysis of the site-projected l -decomposed density of states, charge transfer and charge density shows that bonding is predominantly of ionic nature. We distinguish hybridization between Sc-d states and O - p states in the valence bonding region. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the thermal effect on the lattice constant, bulk modulus, heat capacities and thermal expansion coefficient is calculated.

The isothermal and non-isothermal ageing of an Al-2.4 wt% Cu alloy have been studied using X-ray diffraction analysis and differential scanning calorimetry (DSC) at different heating rates. Quantitative metallography methods have been applied to measure the corresponding transformed volume fractions at various temperatures and times of precipitation. The variation of the heating rate using DSC technique has allowed us to calculate two kinetics parameters of precipitation which are the Avrami exponent and the activation energy of the process using Kissinger, Ozawa and Bosswell methods. These parameters are similar to those found for the precipitation reaction of θ′ and θ (Al2Cu) phases.